The present invention relates in general to flow meters and in particular to a new and useful distribution meter for measuring the relative flow of pulverized coal to a plurality of burners in a coal fired installation.
The use of a pulverized coal/air mixture for firing power plants and the like is known. Coal having a relatively large particle size is provided to a pulverizer where it is ground to a smaller particle size and mixed with air. The air/pulverized coal mixture is then supplied over a plurality of pipes to a plurality of burners in a furnace or boiler.
Details concerning the preparation and use of pulverized coal as a fuel can be found in the publication STEAM, ITS GENERATION AND USE, 39th edition, Babcock and Wilcox Company 1978, at chapter 9.
At the present time it is not standard practice to measure the pulverized coal flow to the burners associated with a given pulverizer on either an absolute or a relative basis.
A current unsolved problem in this field, is that of uneven distribution of pulverized coal (pc) among the several burners served by a single pulverizer. This problem would be expected to be a function of load for a given set of pc distribution parameters and/or a function of time as the pc distribution parameters change. Uneven pc distribution to the burners leads to inefficient burning and poor control of stack emissions. For example, in designing the burner piping, the resistance of the primary air/pc mixture is calculated for each of the burner pipes for the maximum pulverizer load condition. These resistances are then balanced by the use of orifice plates suitably sized and placed in the pipes. Accurate verification of the pc distribution is not presently possible. However, it is known that the hydraulic resistance of the pipes is a function of the load. Thus, even if balanced pc distribution had been achieved at maximum pulverizer loading, the distribution would be unbalanced at a different load. Further, over a period of time the orifice plates (or other resistive elements placed in the pipes to balance the air flow) will wear or erode away; thus, the pc distribution would also change with time. This lack of knowledge (and control) of the pc distribution leads to suboptimum burning efficiency of the fuel and to lack of control of stack emissions. Accurate fuel distribution would enable lower excess air, raise boiler efficiency and reduce NO.sub.x.
Flowing solid/air mixtures are known to have electrostatic and triboelectric properties. This includes a flowing pulverized coal/air mixture. See for example,
P. W. King, "Mass Flow Measurement of Conveyed Solids by Monitoring Intrinsic Electrostatic Noise Levels", Pneumotransport 2, Univ. of Surry, Guildford, Engl., pp D2-9 to D2-20 (Sept. 1973);
I. D. Doig and G. H. Roper, "Fundamental Aspects and Electrostatic Influences in Gas-Solid Transportation Systems", Australian Chemical Engineering, pp. 9-17 (April 1963);
S. L. Soo, "Effect of Electrification on the Dynamics of a Particulate System", Ind. Eng. and Chem. Fundamentals 3, pp. 75-80 (Feb. 1964);
B. N. Cole, M. R. Baum, and F. R. Mobbs, "An Investigation of Electrostatic Charging Effects in High-Speed Gas-Solids Pipe Flows", Proc. Instn. Mech. Engrs. 184 (3C), pp 77-83 (1969-70);
D. J. Montgomery, "Static Electrification of Solids", Solid State Physics 9, Academic Press, N.Y., pp 139-197 (1959);
B. A. Batch, J. Dalmon, and E. T. Hignett, "An Electrostatic Probe for Measuring the Particle Flux in Two-Phase Flow", C.E.R.L. Lab Note. No. RD/L/N 115/63
K. Min, B. T. Chao, and M. E. Wyman, "Measurement of Electrostatic Charge on Solid Particles in Solid-Gas Suspension Flow", The Review of Scientific Instruments 34(5), pp. 529-531 (May 1963); and
E. W. B. Gill, G. F. Alfrey, "Frictional Electrification", Nature 163, p. 172 (Jan. 1947).
Up til now however, no reliable correlation has been found between the sensed electrostatic charge of flowing pulverized coal in particular, and the flow parameters such as velocity, density and mass flow rate.